1. Technical Field
The present disclosure relates to an organic light-emitting display device and a driving method thereof.
2. Discussion of the Related Art
With the advancement of an information-oriented society, various desires for display devices for displaying an image are increasing. Therefore, various display devices, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, organic light-emitting display devices, etc. have been used recently.
Among these display devices, the organic light-emitting display devices are driven with a low voltage and are thin, and have a good viewing angle and a fast response time. The organic light-emitting display devices each include a display panel that includes a plurality of data lines, a plurality of scan lines, and a plurality of pixels respectively provided in a plurality of areas defined by intersections of the data lines and the scan lines, a scan driver that supplies scan signals to the scan lines, and a data driver that supplies data voltages to the data lines. The plurality of pixels each include an organic light-emitting diode (OLED), a driving transistor that controls the amount of current supplied to the OLED according to a voltage at a gate electrode thereof, and a scan transistor that supplies a data voltage of a data line to the gate electrode of the driving transistor in response to a scan signal of a scan line.
Due to differences in processes occurring in manufacturing an organic light-emitting display device or a threshold voltage shift of a driving transistor caused by long-time driving, the threshold voltages and electron mobility of driving transistors of pixels differ. Therefore, when the same data voltage is supplied to the pixels, the currents of the driving transistors supplied to OLEDs should be the same. However, despite the same data voltage being supplied to the pixels, the currents of the driving transistors supplied to OLEDs differ due to a threshold voltage difference and an electron mobility difference between the driving transistors of the pixels. As a result, even when the same data voltage is supplied to the pixels, light emitted from the OLEDs of different pixels have different luminances. To solve such problems, a compensation method of compensating for threshold voltages and electron mobility of driving transistors has been proposed.
The compensation method may be categorized into an “internal” compensation method and an “external” compensation method. The internal compensation method senses and compensates for a threshold voltage of a driving transistor in each pixel. The external compensation method supplies a predetermined data voltage to each pixel and senses a current of the driving transistor through a sensing line according to the predetermined data voltage. Subsequently, the external compensation method converts the sensed current into digital video data and compensates for digital video data to be supplied to each pixel, based on the digital video data obtained through the conversion.
The organic light-emitting display device uses a supply voltage from a power source built into a control printed circuit board (C-PCB) outside a source drive integrated circuit (IC) to generate a sensing voltage and a data voltage necessary for performing the external compensation method and a reference voltage for controlling a luminance of an entire display panel. The source driver IC performs sensing based on the external compensation method by using the voltages supplied thereto.
In the organic light-emitting display devices of the related art, if the sensing voltage is supplied from C-PCB, areas disposed on sides, e.g., a left end and a right end, of the display panel are farther away from the C-PCB than an area disposed on a center of the display panel. Therefore, because a resistance caused by a line is high, a low sensing voltage is supplied. When the sensing voltage is lowered, even when the same data voltage and reference voltage are supplied, compensation is performed differently. Therefore, as time elapses, a difference occurs between the data voltage and the reference voltage. As such, a luminance deviation between areas of the display panel occurs.
Furthermore, in addition to the sensing voltage, the data voltage and the reference voltage are differently supplied, depending on an area characteristic of the display panel. Because the areas disposed on the sides, e.g., the left end and the right end, of the display panel are farther away from the C-PCB than the area disposed on the center of the display panel, when the data voltage and the reference voltage are supplied from the C-PCB, a resistance caused by a line is high. Also, the physical characteristics of pixels provided in the areas disposed on the sides, e.g., the left end and the right end, of the display panel can differ from those of the area disposed on the center. For this reason, luminance in the areas disposed on the sides, e.g., the left end and the right end, of the display panel is more reduced than luminance in the area disposed on the center, causing a luminance deviation between the areas of the display panel.
Particularly, in large organic light-emitting display devices, a physical characteristic difference between the pixels provided in the display panel and a length difference of lines connected between the C-PCB and the display panel occur, causing voltage drop where levels of the sensing voltage, the data voltage, and the reference voltage supplied from the C-PCB are reduced progressively closer to both ends of the display panel. External compensation is sensitive to power supplied to the source driver IC. When the voltage drop occurs, an error occurs in sensing data.
In detail, when the reference voltage is not uniform in the areas of the display panel, a luminance difference occurs. Also, when levels of sensing voltages differ depending on source driver ICs respectively corresponding to the areas of the display panel, noise occurs in the sensing data, causing a defect, such as block dim.